rsqrt

# File lib/mathn.rb, line 120
  def rsqrt(a)
    if a.kind_of?(Float)
      sqrt!(a)
    elsif a.kind_of?(Rational)
      rsqrt(a.numerator)/rsqrt(a.denominator)
    else
      src = a
      max = 2 ** 32
      byte_a = [src & 0xffffffff]
      # ruby's bug
      while (src >= max) and (src >>= 32)
        byte_a.unshift src & 0xffffffff
      end

      answer = 0
      main = 0
      side = 0
      for elm in byte_a
        main = (main << 32) + elm
        side <<= 16
        if answer != 0
          if main * 4  < side * side
            applo = main.div(side)
          else
            applo = ((sqrt!(side * side + 4 * main) - side)/2.0).to_i + 1
          end
        else
          applo = sqrt!(main).to_i + 1
        end

        while (x = (side + applo) * applo) > main
          applo -= 1
        end
        main -= x
        answer = (answer << 16) + applo
        side += applo * 2
      end
      if main == 0
        answer
      else
        sqrt!(a)
      end
    end
  end